COMMUTATION TRANSIENTS IN SELF-CONTROLLED SYNCHRONOUS MACHINES CONNECTED TO D.C. NETWORKS

ABSTRACT

In this paper the commutation phenomenon in a synchronous machine (generator or motor) associated with a thyristor bridge is studied. The transient analysis of the different currents in the different windings is done for a salient pole synchronous machine with damper windings. The different expressions are given in terms of the classical machine reactances and time constants which can be directly measured or furnished by the manufacturer. Comparison between theoretical and practical results are given.     

THERMAL ANALYSIS OF LARGE OIL-IMMERSED TRANSFORMER WINDINGS

ABSTRACT

A method of numerical thermal analysis of large oil-immersed transformer windings is presented. The analysis consists of two steps: first, the leakage magnetic field is solved in the windings; second, the basic and additional losses distribution is calculated simultaneously with temperature rise distribution in the cross-sections of individual coils allowing for special geometries and cooling conditions of different types of windings. An example of the analysis is given and the values calculated are compared with the results of factory tests.     

Air temperature effect on thermal models for ventilated dry-type transformers

The temperature of the air surrounding the windings of ventilated dry-type transformers is an important factor in the cooling of the windings since they are cooled only by the air. In particular, inner windings are sensitive to the air temperature in vertical cooling ducts. This study presents air temperature effect on the temperatures in foil-type inner winding for the dry-type transformers. A transformer rated at 2000 kVA was selected for the research and temperature distribution was calculated under constant and varying air temperatures inside vertical ducts at three different loads. The 2-D transient heat diffusion equation was solved using the finite element method by coupling it with the vector potential equation due to non-uniformly generated heat caused by eddy currents in the foil winding. The calculated temperatures at constant and varying air temperatures are presented together with experimental values. The numerical and experimental results of this study showed that the air temperature affects the accuracy of temperatures in foil-type inner winding greatly.     

HARMONIC ANALYSIS OF INDUCTION MOTORS WITH STATOR FAULTS

ABSTRACT

In the paper stator faults are analyzed by means of a procedure based on the space-vector theory. The used approach, due to Stepina, allows to consider separately each conductor of every single slot and therefore to take easily into account the winding dissymmetry.

The interactions among the different harmonic fields are studied by starting from the topological structure of windings and the harmonic analysis of the currents and of torque Is carried out.

The method is tested to numerical computations of steady-state currents for an induction machine with different positions of stator short-circuits.

Finally the procedure is validated by using an experimental squirrel cage machine, having stator windings constructed so as to realize different short-circuits.     

OBSERVATIONS ON THE DESIGN OF DISTRIBUTED ARMATURE WINDING BY POLY PHASE SYMMETRISATION

ABSTRACT

The generalised process of designing distributed poly-phase armature windings by the technique of symmetrization offers special advantages in developing dedicated machines for operation with non-sinusoidal supplies.

Principles of symmetrization have been reviewed with special reference to 3-phase windings and important rules governing the applications of the process have been enumerated, both with reference to single-speed balanced and unbalanced windings as well as multi-speed windings.

Although such special windings in general, have wider harmonic spectra compared to standard designs, a judicious selection of symmetrised windings can, in fact prove beneficial in specific cases. The paper attempts to lay down the procedure for systematic design of 3-phase symmetrised windings.     

Some Aspects of Temperature Rises in a Natural Cooled Oil-Filled Three-Phase Transformer

ABSTRACT

By means of measurements on a small core type oil filled transformer the possibility of the following methods of determining winding temperature have been examined: (a) Use of lumped constant coefficients for steady—state prediction; (b) Use of the superposition of open circuit and short circuit temperaturerises to give the rises for the corresponding load test.It is seen that (a) gives reasonable results but that (b) gives higher temperatures than those measured on the load test. Finally the assumption of all heat absorbed in the windings over a short circuit is seen to be valid.     

DIFFERENTIAL LEAKAGE OF FRACTIONAL-SLOT WINDING

ABSTRACT

This paper contributes a large number of differential leakage factors of fractional-slot windings calculated by the computer. Based on the results, a set of new leakage factor curves is given. These curves are not only more accurate and complete than those given by M.M. Liwschitz, but easier to use as well. For any number of slots per pole per phase less than 5, the differential leakage factor of a symmetrical fractional slot winding can be determined for the machine design purpose     

A MATHEMATICAL MODEL OF THREE-PHASE INDUCTION MACHINES

ABSTRACT

A technique for studying the behaviour of three-phase, wound-rotor induction machines under both transient and steady-state conditions is described. It is arranged to cope with both non-sinusoidal winding distributions and non-linear operation of the magnetic paths. Because such conditions prevent simple expressions from being obtained when transformations are made to produce a two-axis equivalent model, the present analysis is based on the actual machine windings. The basic equation. |v| = |z| |i| is solved for each time step after the appropriate values of the elements in the impedance matrix have been determined by examining the magnetic conditions around the air gap periphery.

The results of particular studies are given.     

DESIGN PROCEDURE FOR A SMALL SELF-CONTROLLED INVERTER-FED SYNCHRONOUS MACHINE WITH A PERMANENT MAGNET ROTOR

ABSTRACT

The object of the paper is the analytical study of a small permanent magnet inverter fed synchronous machine in order to find an optimal design. The inside flux density created by both the stator windings and the rotor magnet is calculated. This allows the design of the stator of the machine. Then, the variation of the torque as a function of the inner diameter is derived for a given outer diameter of the rotor (6.5 mm) leading to the rotor dimensions. Our final choice has been 2.75 mm corresponding to a torque of 68 10^?4 mN (experiment: 69). Nominal speed is around 6000 rpm for a 12 V direct current supply voltage. A simple model of the machine is developed and results are shown.     

EMF AND INDUCTANCES OF A TRANSFER FIELD SYNCHRONOUS MACHINE

ABSTRACT

This paper further develops the theory of the TF machine and examines the waveform of emf, and also the inductance variations of the machine, and compares these with test results. It is shown that it is possible, without special rotor profiling or the use of chorded or specially connected windings, to obtain in this machine inductance variations similar to those of a well designed, conventional, cylindrical rotor synchronous machine. This is also a necessary condition for satisfactory dc operation. The emf of such a machine would, for all practical purposes, be regarded as free of harmonics.     

感应电动机定转子全域温度场数值计算及相关因素敏感性分析

提出了针对无轴向通风冷却电机温度场计算的新思想，合理处理了电机定子与气隙之间以及转子与气隙之间复杂的对流散热过程， 妥善解决了定、转子之间的热交换问题。给出了散下线定子绕组的等效热模型，简化了计算难度并且节省了计算时间。在此基础上建立了笼型感应电动机定、转子全域温度场二维数学模型和二维有限元计算模型。计算了电机额定负载运行时定、转子的稳态温度场以及气隙温降；实验结果验证了该电机温度场计算模型的合理性和计算结果的正确性。在该温度场计算模型的基础上，分析了电机温度场对定子铜耗、散热翅高度以及定子绕组浸渍质量等相关因素的敏感性，为电机优化设计奠定理论基础。     

MODIFIED ASYNCHRONOUS CASCADE MACHINE SYSTEM

ABSTRACT

The modelling of the modified asynchronous cascade machine system is done in order to study the features of such system under field-oriented frame of reference. The modified machine system has two stator windings and two sections of rotor winding on the same shaft One of the stator windings is connected to the ac network while the other winding is connected to an inverter capable of controlling power flow in both directions. This system can be operated in a wide speed range and both sections of the rotor winding can produce useful torque.     

CORRESPONDENCE: A TRAVELLING WAVE ENERGY CONVERTOR

ABSTRACT

A variable speed single phase linear induction motor having series connected windings and shunt connected capacitors which, as in an artificial transmission line, produce a travelling magnetic field, can be used as a low speed asynchronous generator. A small model of such a machine has been investigated.     

CORRESPONDENCE: THE FLUX-BRIDGE MACHINE

ABSTRACT

This note describes a new kind of electromagnetic machine whose action is based on the change of flux linkage between two stationary coils-field and armature coils-when a segmental rotor moves between them. The machine differs from conventional inductor machines in having a dynamic component of emf in addition to the usual pulsation component, and also the windings are disposed on separate machine members. The basic principles are outlined and simple analysis is attempted. Possible modes of application are proposed.     

ANALYTICAL APPROACH TO THE OPERATION OF A SYNCHRONOUS MACHINE ASSOCIATED WITH A THYRISTOR BRIDGE

ABSTRACT

A synchronous machine associated with a thyristor bridge operates normally under unbalanced conditions which are described and studied in the present paper. Natural cut-off thyristors is used in the present system where the gates of thyristors are controlled by the rotor position. It is assumed that the machine has salient poles and damper windings. Both motor and generator operations are contemplated.

An analytical approach has been used, and the exact shape of the currents has been considered. The commutation problem is studied in detail, taking into consideration the transient effects of the armature circuits and the limited value of the smoothing reactor. The different expressions are given in terms of the classical machine constants which can be directly measured or furnished by the manufacturer. Comparison between theoretical and practical results are given.     

TRANSIENT EQUATIONS AND D,Q AXIS EQUIVALENT CIRCUIT OF A SUPERCONDUCTING GENERATOR

ABSTRACT

A set of equations which represent the transient performance of a superconducting generator are presented in this paper. Based on a three-dimensional analysis of an air-core machine with helical windings, the transient equations in the form of Fourier transforms are developed. In this calculation, the skin effect and the of eddy currents in shielding elements are taken into representative example transient is worked out.     

TWO-DIMENSIONAL WINDING MODELS FOR THE CALCULATION OF MAGNETIC FIELDS IN SUPERCONDUCTING TURBOGENERATORS

ABSTRACT

This paper, with reference to a two-dimensional study of the magnetic field of alternators with superconducting field windings, analyses the models of field and armature windings of the machine. Using tentative designs of two high -rating generators (respectively two-pole (P ? 1200 MVA) and four-pole (P?1500WA)) the authors show numerical differences which the adoption of the models brings about on the calculation of the components of the magnetic field inside the generator.     

UNIFIED ANALYSIS OF THE SHORT CIRCUIT TRANSIENT OPERATIONS OF SALIENT POLE SYNCHRONOUS MACHINES

ABSTRACT

A general analysis for the different cases of short circuits of a synchronous machine is given in this paper. The effects of saliency and of damping circuits are considered. Expressions for the transient currents in the machine windings, flux linkages, open phase voltages and electromagnetic torques are given in the case of any short circuit. The different formulae are given in terms of the machine pameters which can be measured by classical tests, and are generally given by the manufacturer- Experimental verifications have been made on a conventional salient pole machine and are given for all kinds of short circuits over all the possible range of the rotor axis positions at the instant of short circuit.     

EXACT RELATIONSHIPS BETWEEN PARAMETERS AND TEST DATA FOR MODELS OF SYNCHRONOUS MACHINES

ABSTRACT

In a recent paper the authors have presented a new method expressing the parameters of a synchronous machine model in terms of measurable time constants, without the traditional simplifying assumptions. The considered model is characterized by equal mutual reactances between armature, field and damper windings.

This paper shows the extention of the new method to the models with all three unequal mutuals and with two equal mutuals. The exact relationships between the parameters of the examined models and the test data are provided. Comparisons are made between new and old method results to demonstrate the discrepancies in values of parameters.